Aluminum is an important alternative material to steels for the automotive and other industries due to its superior strength-to-weight ratio. One of the most common joining processes for aluminum is gas metal arc welding (GMAW). In GMAW an electrode creates an arc, and a continuously fed wire electrode is melted by the arc and transferred to the welding pool between the two aluminum workpieces.
Compared to other joining processes, GMAW has many advantages in achieving quality of weld joints and efficiency of production. However, GMAW is a very complicated process involving mechanical, electrical, thermal, chemical and metallurgical phenomena. Thus it can be challenging to maintain stability.
Furthermore, aluminum is much more difficult to weld than steel and is more likely to have weld discrepancies compared to steels. For example, compared to steels, aluminum has higher thermal conductivity, higher rate of thermal expansion and higher solidification shrinkage, thus requiring more intense and tighter controls of heat input. Aluminum also has much higher hydrogen solubility, which results in higher sensitivity to the shielding gas.
In order to ensure GMAW process consistency and weld quality, when welding aluminum as well as other metals, it would be desirable to develop improved on-line weld monitoring methods by which the available process data, such as weld voltage, could be evaluated in a manner that process instability and weld discrepancies could be detected quickly, thus enabling prompt adjustment of weld variables such as arc length, wire feed rate, shielding gas composition and flow rate, welding power source characteristics, in order to bring the welding process back into proper consistency and quality.